The present invention relates to magnetic media in general, and more particularly, to magnetic media and method for data verification.
Counterfeiting and fraud with magnetic media have been known for a long time and various techniques to combat this crime have been employed. The "Watermark" technology by Malco/Thorn/EMI is an example of a magnetic security technology which has been available for a number of years. One of the disadvantages of the "Watermark" technology is that it requires special magnetic media to be manufactured with security features built in. This has proven to be too costly for any large scale employment of the technology.
Another security system for magnetic media is disclosed in U.S. Pat. No. 4,837,426 ('426) by Pease, Copella, and Flannery. This system uses random variations in the amplitude of the output signal from a low noise amplifier reading the magnetic media to variations in the coercivity of any media to provide security data. Unfortunately this technique uses amplitude ratios to develop the security data so counterfeiting and copying may be relatively easily accomplished through the use of such techniques as high frequency bias recording.
Yet a third security system is disclosed in U.S. Pat. No. 4,650,978 ('978) by Hudson and Fernandez. The '978 patent teaches the use of the natural random variations in the magnetic properties of the media, caused by variations in coercivity, and granularity, coating thickness, surface profile and, most specifically, the random variations in the hysteresis of the medium and its past magnetic history to provide security. However, it involves the use of analog patterns which are complex and expensive and hard to. analyze. Interfacing with existing systems is difficult because of space occupied on the circuit card, to fully utilize the technology. Furthermore, it requires the use of expensive circuitry such as A/D convertors.
It is accordingly a general object of the invention to provide a method for data verification and magnetic media therefor that overcomes the difficulties of the prior art methods and media.
It is a specific object of the invention to provide a data verification method and magnetic media that utilizes digital techniques to establish and decode a security magnetic sequence on and from the magnetic media.
It is a feature of the invention that the data verification method can be implemented with relatively inexpensive digital circuitry.
It is another feature of the invention that the reliability of data decoding is enhanced through the use of digital recording and processing techniques.